The present invention relates to a screw compressor for compressing a gas such as a refrigerant.
Semi-closed type screw compressors have been widely used recently. This semi-closed type screw compressor is so constructed that a motor section and a compression section are placed in a casing, with a motor shaft of the motor section and a screw shaft of the compression section provided as an integral unit, where the refrigerant is sucked into a compression section through the motor section.
However, in this semi-closed type screw compressor, since the refrigerant is sucked into the compression section through the motor section, the refrigerant is heated by the motor, causing a problem of deteriorated efficiency.
Therefore, such an open type screw compressor as shown in FIG. 2 is reviewed. This open type screw compressor assembly is so constructed that a motor 2 and a screw compressor 3 are mounted on a large-sized bed 1, while a shaft 2a of the motor 2 and a shaft 3a of the screw compressor 3 are coupled to each other with a coupling 5.
However, in this open type screw compressor, since the motor 2 and the screw compressor 3 are provided as completely separate units, the large-sized bed 1 and the coupling 5 are involved while the alignment between the shaft 2a of the motor 2 and the shaft 3a of the screw compressor 3 takes man-hours, thus resulting in a problem of quite high costs.
Accordingly, an object of the invention is to provide a screw compressor in which the needs for the bed and the coupling are eliminated, therefore the need for alignment being also eliminated, and yet in which the gas is not heated by the motor.
In order to achieve the above object, in a first aspect of the invention, there is provided a screw compressor in which a compression section and a motor section are placed in a casing, comprising:
a gas passage passing only through the compression section; and
a main shaft to which a rotor of the motor section and a screw of the compression section are fixed.
In this screw compressor of the first aspect of the invention, since the compression section and the motor section are placed inside the casing, the casing plays the role of a bed, eliminating the need for the bed. Further, since both the rotor of the motor section and the screw of the compression section are fixed to one main shaft, the need for the coupling of the prior art is eliminated, so that the man-hour for alignment is eliminated. As a consequence, this screw compressor can be manufactured with low cost and can be installed simply.
Further, since the gas passage passes only through the compression section and not through the motor section, gas is never heated by the motor of the motor section. As a consequence, this screw compressor is good at compression efficiency.
In one embodiment, the main shaft is supported at three points by bearings provided at three sites of an end portion of the motor section, an end portion of the compression section and a site between the motor section and the compression section.
According to this embodiment, since the main shaft is three-point supported by the bearings provided at the three points, the number of rolling bearings involved is reduced and the assembly is also facilitated. As a consequence, this screw compressor can be manufactured with low cost.
In one embodiment, a motor-cooling air passage is provided in the casing and air blown by a fan that is driven by a motor of the motor section passes through the motor-cooling air passage.
According to this embodiment, the air blown by the fan passes through the motor-cooling air passage to cool the motor. As a consequence, coils of the motor can be prevented from elevating in temperature.
In a second aspect of the invention, there is provided a screw compressor comprising:
a casing which is internally partitioned into a first chamber and a second chamber opposed to each other;
a screw type compression section placed in the first chamber;
a motor section placed in the second chamber and having a motor for driving the compression section;
a gas passage defined in the first chamber and allowing a gas to flow from an inlet only through the compression section to an outlet; and
a motor-cooling air passage defined in the second chamber and allowing air to pass from an inlet only through the motor section to an outlet, wherein
the gas passage and the motor-cooling air passage are independent from each other, and
a main shaft to which a rotor of the motor is fixed has an extended portion axially extended, and the screw of the compression section is fixed to the extended portion.
According to the screw compressor of the second aspect of the invention, since the compression section and the motor section are placed in the first chamber and the second chamber, respectively, defined in the casing, the casing plays the role of a bed, eliminating the need for the bed. Also, since both the rotor of the motor section and the screw of the compression section are fixed to one main shaft, the need for the coupling of the prior art is eliminated, so that the man-hour for alignment is also eliminated. As a consequence, this screw compressor can be manufactured with low cost, and can be installed simply.
Further, since the gas passage passes only through the compression section and not through the motor section, gas is never heated by the motor of the motor section. As a consequence, this screw compressor is good at compression efficiency.
One embodiment further comprises a fan driven by the motor provided at a vicinity of the inlet of the motor-cooling air passage, wherein air blown by the fan is allowed to flow to the motor-cooling air passage.
According to this embodiment, the air blown by the fan passes through the motor-cooling air passage to cool the motor. As a consequence, coils of the motor can be prevented from elevating in temperature.
In one embodiment, the screw of the compression section is a single screw.